Issues with a couple of keys

[Bob Proulx]

rsbecker at nexbridge.com wrote:
> Thorsten Glaser wrote:
> >The Doctor wrote:
> >> Anyone having problems with delete or backspace in ssh?
> >
> >No, but this sounds like the age-old issue.

Yes.  The age-old issue.

Just recently I ran into a different user that had just switched to
using qterminal and hit this problem.  It seems that qterminal (among
others) sends Control-H (BS) as the erase character instead of what
today I would call the ad-hoc standard DEL character.  Which of course
causes problems.  I was surprised that this was still "a thing" yet
here is a ticket on it.

    https://github.com/lxqt/qterminal/issues/770

Also I was surprised that upstream XTerm also uses ^H instead of DEL
and had been protected from this by Debian patching it.

    https://salsa.debian.org/xorg-team/app/xterm/-/blob/debian-unstable/debian/patches/900_debian_xterm.diff

Therefore it seems that this age-old issue is yet again still causing
problems.  What's old is new again.

> >Make sure your tty settings match the termcap *and* terminfo entries for your
> >$TERM *and* match the actual terminal used on the client.
> >
> >More specific help depends on which client and server OS and terminal is used.
>
> I have seen this for years, including having DEL and BS get into
> passphrases. I seriously thought this was a deliberate feature.

Configurable tty parameters are a feature.  But with power comes
responsibility.  An earlier default was '#' which makes it difficult
to type in that key.  But it is a configurable setting.

To help, and to confuse, the very popular bash command line shell
accepts either BS or DEL for erase regardless of tty setting.  Which
tells me that is not the command shell on the remote system.

To make this more useful for The Doctor try determining what erase
character is being sent by your terminal emulator.  Set it to
something different such as @ and then type into od and have it
print out the raw hex value of the key from the keyboard being
pressed.

    $ stty erase @
    $ od -tx1
    ^?    <-- Press the Backspace key, followed by Enter
    ^d  <-- type in Control-D here to end input
    0000000 7f 0a

The 7f is DEL (the 0a is linefeed LF from Enter) and my keyboard is
configured to produce DEL when pressing Backspace.  On a different
terminal configured to emit BS this will be the result.

    $ od -tx1
    ^H    <-- Press the Backspace key, followed by Enter
    ^d  <-- type in Control-D here to end input
    0000000 08 0a

The 08 is the BS character.  Again 0a is the LF from Enter.

The terminal erase character can be reset to normal.  But if it is
bash/ksh/zsh/tcsh then one must quote it Control-V before pressing the
Backspace key so that it inserts the next key verbatim.  Since those
ignore the tty erase parameter and always accept either for erase.  On
strict sh though since the erase is not set pressing Backspace will
display ^?  or ^H directly without quoting verbatim with Control-V
which is a ksh/bash/zsh/tcsh thing.

Easier just to exit the terminal and let it evaporate.  Just exit it!
Open a new terminal which then uses the default erase again.

After determining the erase character sent by your terminal emulator
(does anyone use actual terminals these days?) then you can set it on
the system in the same way that it was set above to reset the terminal.

    stty erase ^?
Or
    stty erase ^H

In the old days we would have to put this in a case statement based
upon our $TERM setting and other hints so as to select the right thing
for that terminal.  Those were dark bad days indeed.  I had hoped to
never see those days again hoping that DEL (^?) had won.

Bob